1. Field of the Invention
The present invention relates to a display and more specifically to a display such as a liquid crystal display and the like, which includes an anisotropic scattering film.
2. Description of the Related Art
As a typical example of a display in which there is the dependency of display performance on the viewing angle (a viewing angle characteristic), a liquid crystal display typified by a twisted nematic (TN) mode is known. Incidentally, the term “there is the dependency of display performance on the viewing angle” means that display performance such as a contrast ratio, a gradation characteristic and chromaticity differs between the cases of viewing from the front (the direction of the normal to a viewing screen of the display, the direction of a viewing angle of 0°) and viewing obliquely (the direction in which a viewing angle is larger than 0°). Generally, it is known that these display performance in the case of viewing obliquely is inferior to that in the case of viewing from the front.
In a TN mode liquid crystal display, a contrast ratio decreases gradually as the viewing angle is increased in a vertical or horizontal direction (three, six, nine or twelve o'clock direction). For example, even when a contrast ratio is 320 in viewing from the front, a contrast ratio is 10 in viewing at angle of 75° in an upper direction (twelve o'clock direction), in viewing at viewing angle of 50° in a lower direction (six o'clock direction), in viewing at angle of 65° in a left direction (nine o'clock direction), and in viewing at angle of 68° in a right direction (three o'clock direction). In addition, a display color is neutral (not tinged) in viewing in the front direction but it is tinged with yellow in viewing in the upper, lower, left or right direction. Particularly, in the case of viewing in the lower direction, an abnormal phenomenon of a gradation characteristic referred to as a gradation reversal, in which a display image looks reverse in video, may be observed. Such the viewing angle dependency of display performance in a liquid crystal display results from the optical anisotropy of components such as anisotropy of the refractive index of a liquid crystal molecule, a polarization absorption property and a polarization transmission property of a polarizing plate and the like and it is said that the viewing angle dependency of display performance is a property inherent in the liquid crystal display.
As a method of improving the viewing angle dependency of the display performance of a liquid crystal display, various methods have been proposed. As such methods, for example, a pixel division method (there are a Half Tone Gray Scale method in which a pixel is split into multiple sections and voltages applied to pixels are changed in certain proportions and a Domain Division method in which a pixel is split into multiple domains and liquid crystal alignment is controlled separately in each domain), display modes such as an In-Plane Switching (IPS) mode in which an electric field is applied to a liquid crystal laterally, a Multi-domain Vertical Alignment (MVA) mode in which a liquid crystal being vertically aligned when an voltage is not applied is driven and an Optically Compensated Birefringence (OCB) mode in which a bend aligned cell and a retardation film are combined, and an optical compensation method using the retardation film are proposed, and it is also investigated to use these methods appropriately in combination and many liquid crystal displays which have been commercialized employ these methods.
However, in these methods, there were rooms for improvement in that when the pixel division method or the above-mentioned display mode is employed, it is necessary to modify an alignment layer, a structure of an electrode and the like and establishment of the production technology and installation of the production facilities for this modification are required, and this results in the difficulties in production and the high cost. In addition, its effect of improving the viewing angle dependency is not sufficient. Further, also in the optical compensation method using the retardation film, its effect of improving the viewing angle dependency is limited. For example, since the most suitable value of phase difference for compensating a phase difference of a liquid crystal cell varies between the cases of displaying white and black, it is impossible to compensate a phase difference of a liquid crystal cell in both display of white and display of black by the optical compensation method. In addition, there was a room for improvement in that a compensation effect of the retardation film is not attained at all in the axial azimuths of the polarization axes (transmission axis and absorption axis) of a polarizing plate in principle and an effect of improvement is limited to the range of specified azimuth angles.
As a method of improving the viewing angle dependency of the display performance of a liquid crystal display besides the above methods, a method of providing a scattering film on the viewing screen side of a the liquid crystal display element to level the outgoing lights is known. This method can be applied to all display modes and modification of a structure of a display cell is basically unnecessary. In addition, it is possible to attain an effect in both states of displaying white and black as opposed to the optical compensation method using the above retardation film and its effect does not disappear in the azimuths parallel to the polarization axes of a polarizing plate.
In addition, as a light source of a commonly used liquid crystal display, a diffusion backlight system emitting diffused lights is employed. Since most of liquid crystal display modes or polarizing plates show best properties for vertical incident lights, lights from the diffusion backlight system is collimated as far as possible by a lens film or the like and is vertically inputted into a liquid crystal display element (a liquid crystal cell). Thereby, a furthermore effect of improving the viewing angle dependency can be attained and therefore many technologies concerning this diffusion backlight system are proposed.
However, since a method of obtaining collimated lights simply and efficiently has not been yet established, a method of an improvement in the viewing angle dependency by a scattering film is employed practically in combination with a diffusion backlight system as described above. In this case, an effect of improving the viewing angle dependency can be attained as described above, but there was a room for improvement in that light leakage increases in the front direction and the contrast ratio in the front direction is reduced by a large amount since a part of leaked light obliquely entering and exiting the liquid crystal cell is angled to the front direction by the scattering film in a state of displaying black. This is caused because the scattering property of the scattering film to transmitted light does not varies so much even when changing the incidence angle more or less due to the isotropic scattering performance of the scattering film.
For theses situations, light control plates fabricated by irradiating ultraviolet light from a linear light source within a prescribed angular range, to a resin composition consisting of a plurality of compounds, each of which has a refractive index differing from one another and one or more photopolymerizable carbon-carbon double bonds in a molecule and by curing the resin composition are disclosed in Japanese Kokai Publication Sho-63-309902, Japanese Kokai Publication Sho-64-40903, Japanese Kokai Publication Sho-64-40905, Japanese Kokai Publication Sho-64-40906, Japanese Kokai Publication Sho-64-77001, Japanese Kokai Publication Hei-1-147405, Japanese Kokai Publication Hei-1-147406, Japanese Kokai Publication Hei-2-51101, Japanese Kokai Publication Hei-2-54201, Japanese Kokai Publication Hei-2-67501, Japanese Kokai Publication Hei-3-87701, Japanese Kokai Publication Hei-3-109501 and Japanese Kokai Publication Hei-6-9714, and liquid crystal displays fitted with such light control plates are disclosed in Japanese Kokai Publication Hei-7-64069 and Japanese Kokai Publication No. 2000-180833. These light control plates selectively scatters light entering at a specific angle. Accordingly, it is thought that the reduction in the contrast ratio in the front direction described above can be resolved to some extent by use of this light control plate.
However, it is thought that as shown in FIG. 30, in this resin cured article of the light control plate 50, plate-like regions 40 having refractive indexes different from those of surrounding regions are formed in parallel with one another in conformity with the length direction of a linear light source 51 being located above the light control plate 50 in fabricating the light control plate 50. Thus, when the light control plate 50 is rotated about the A-A axis along which the plate-like regions 40 alternately appear, the incidence angle dependency of the scattering property which the light control plate 50 exhibits is little recognized, but when the light control plate 50 is rotated about the B-B axis along which the refractive index does not change and is uniform, the incidence angle dependency of the scattering property is recognized.
FIG. 31 is a schematic diagram showing the incidence angle dependency of the scattering property which the light control plate 50 in FIG. 30 exhibits. A vertical axis represents a linear transmitting light quantity being an indicator of a degree of scattering. A horizontal axis represents an incidence angle. A solid line and a broken line in FIG. 31 represents the case of rotating the light control plate 50 about the A-A axis and B-B axis in FIG. 30, respectively. In addition, the plus and minus signs of the incidence angle represent the directions of rotation.
The linear transmitting light quantity expressed by the solid line in FIG. 31 is small and nearly constant in both of a front direction and an oblique direction. This means that the light control plate 50 is in a state of scattering irrespective of the incidence angle in rotating the light control plate 50 about the A-A axis. In addition, the linear transmitting light quantity expressed by the broken line in FIG. 31 becomes smaller in the direction close to incidence angle of 0°. This means that the light control plate 50 is also in a state of scattering for light in a front direction in rotating the light control plate 50 about the B-B axis. Further, in the directions where the incidence angle is large, the linear transmitting light quantity expressed by the broken line in FIG. 31 increases. This means that the light control plate 50 is in a state of transmitting for light in an oblique direction in rotating the light control plate 50 about the B-B axis.
Thus, in the previous light control plate, reduction in the contrast ratio in the front direction can be somewhat prevented, but there was a room for improvement in that an effect of improving the viewing angle dependency can be attained only in a specific azimuth since an anisotropic scattering property (a property in which the scattering property varies when an incidence angle is changed) can be attained only in a specific azimuth.